Solution 1:

I use group policy preferences for this. The area you care about is located under user -> preferences -> windows settings -> drive maps.

Here is a howto: http://blogs.technet.com/b/askds/archive/2009/01/07/using-group-policy-preferences-to-map-drives-based-on-group-membership.aspx

EDIT: Just saw that you are using server 2003. In that case, off the top of my head you could you use regular group policy to create a login script to map with net use x: \server\share and scope it to an OU.